Overload preventing device

An overload preventing device which is mounted in a mobile work machine which includes a running body which runs freely, a revolving base disposed on the running body to revolve horizontally, a boom disposed on the revolving base to be derricked, and a plurality of outriggers capable of setting an overhanging width in plural stages, the overload preventing device comprising:

• a storage unit which stores lifting performance data in which a lifting performance is set for each operation state and performance region data in which a switching angle is set to define a performance region which includes a front region, a back region, and a side region;
• and
• a work machine control unit which controls an operation of the mobile work machine on the basis of the lifting performance corresponding to a present operation state of the mobile work machine and an actual load, wherein
• the operation state includes a work radius and an overhanging state of the outriggers,
• the lifting performance includes a first lifting performance which is set to the front region and the back region, a second lifting performance which is set to the side region except a transition region in a case where the outriggers are in different states, and a third lifting performance which is set to the transition region,
• the switching angle includes a first switching angle which defines a boundary between the front region and the side region and a boundary between the back region and the side region in a case where the outriggers are in different states, and a second switching angle which defines the transition region in the side region,
• the first lifting performance and the second lifting performance are set on the basis of the operation state, a stability calculation, and a strength factor of the mobile work machine,
• the third lifting performance is expressed by an interpolation function which is calculated on the basis of an interpolation performance which is interpolated in stages between the first lifting performance and the second lifting performance and a limit value of a revolving angle range corresponding to the interpolation performance,
• the storage unit stores the interpolation function for each overhanging state of the outrigger as the lifting performance data, and
• the first switching angle and the second switching angle are calculated on the basis of the interpolation function, the first lifting performance, and the second lifting performance.